TERMINAL STRUCTURE OF UNSTEADY CLASSICAL AND INTERACTING BOUNDARY-LAYERS

The terminal structure of the unsteady boundary-layer equations is inv estigated for the problem of impulsive flow past a circular cylinder. It is known that both the classical and interacting boundary-layer equ ations for this problem are singular and the singular structure for th e interacting boundary layer on a circular cylinder has not been prope rly resolved using the classical finite difference approach within an Eulerian framework. The objective of this paper is to resolve the sing ular structure for both the classical and interacting boundary layers for the impulsively started flow past a cylinder. An adaptive-grid sch eme, coupled to a panel method for the interacting case, is employed t o resolve the extremely small time and length scales associated with a terminal structure defined by the emergence of a singularity. Calcula tions performed in an Eulerian coordinate system show that interacting boundary-layer calculations terminate sooner than the classical bound ary-layer calculation, and as the Reynolds number decreases, the singu larity occurs earlier in time and closer to the rear stagnation point of the circular cylinder. Comparisons with previous Lagrangian and fix ed-grid Eulerian results are discussed. (C) 1996 American Institute of Physics.